Republican Sen. John McCain left no doubt Monday that he was thinking of President Donald Trump as he criticized the draft system during Vietnam for forcing low-income Americans to serve while the wealthy could avoid war with a doctor's note.

Republican Sen. John McCain left no doubt Monday that he was thinking of President Donald Trump as he criticized the draft system during Vietnam for forcing low-income Americans to serve while the wealthy could avoid war with a doctor's note.

President Trump speaks at Fort Myer in Arlington Va., Monday, Aug. 21, 2017, during a Presidential Address to the Nation about a strategy he believes will best position the U.S. to eventually declare victory in Afghanistan (AP Photo/Carolyn Kaster)

President Donald Trump, hours after Sen. John McCain delivered a speech that repudiated the President, warned the Arizona Republican to "be careful" because at some point he will "fight back."

Just one day after Arizona Sen. John McCain, the chairman of the Senate Armed Services Committee, criticized an American operation in Yemen that left a U.S. service member dead, President Donald Trump took to Twitter to express his opinion on McCain's assertion that the mission was not a success.

Just one day after Arizona Sen. John McCain, the chairman of the Senate Armed Services Committee, criticized an American operation in Yemen that left a U.S. service member dead, President Donald Trump took to Twitter to express his opinion on McCain's assertion that the mission was not a success.